Add SDK level check to adding sandbox UIDs.

ConnectivityServiceTest builds against the latest Vpn framework code,
but when run on an older base image (eg 'S'), said framework code might
run into runtime errors calling new APIs. Until the test is decoupled,
do the SDK level check here.

Bug: 230548427
Bug: 232420362
Test: Build
Change-Id: If453e16e680f46cf2b9eb769e5607fb5513b32ac
(cherry picked from commit ab678b98)
Merged-In: If453e16e680f46cf2b9eb769e5607fb5513b32ac